* May WCS seen at $13.50/bbl under WTI
* May synthetic last trades at $7.50 over WTI
CALGARY, Alberta, April 10 (Reuters) - Canadian oil prices moderated on Wednesday as planned refinery work cut into demand.
Western Canada Select heavy blend for May delivery last traded at $13.50 per barrel below West Texas Intermediate crude, according to Shorcan Energy Brokers. WCS settled on Tuesday at $12.15 below the benchmark.
The widening differential comes as Suncor Energy Inc said it had started planned maintenance at its 140,000 barrel per day refinery at Edmonton, Alberta.
The refinery relies on heavy crudes from the oil sands for its feedstock.
Also on Wednesday, Phillips 66 said it had completed planned maintenance at the 356,000 bpd Wood River, Illinois, refinery it co-owns with Canadian oil sands producer Cenovus Energy Inc.
The work, which included an overhaul of a crude distillation unit and coker units, began in the last week of February.
Light synthetic crude from the oil sands for May delivery last traded at a premium of $7.50 per barrel above WTI, down from a settlement price on Tuesday of $8.80 above the benchmark.
Synthetic crude generally trades close to WTI, however prices have been buoyed as planned maintenance at upgraders owned by Suncor and Canadian Natural Resources Ltd is expected to cut into supply.